diff --git a/test/registered/unit/mem_cache/test_hiradix_pp_sync_drain.py b/test/registered/unit/mem_cache/test_hiradix_pp_sync_drain.py
index 7ff6dc795..ea77f0378 100644
--- a/test/registered/unit/mem_cache/test_hiradix_pp_sync_drain.py
+++ b/test/registered/unit/mem_cache/test_hiradix_pp_sync_drain.py
@@ -56,6 +56,7 @@ class TestUnifiedPPSyncBatching(unittest.TestCase):
         cache.pp_size = 2
         cache.enable_storage_metrics = False
         cache.storage_metrics_collector = None
+        cache.buffer_pipeline = None
         cache._drain_async_work = MagicMock()
         cache._all_reduce = MagicMock()
         cache.writing_check = MagicMock()